Process for the manufacture of olefins



Sept. 5, 1939. A. J. VAN PEsKl PRocEss Foa THE MANUFAGTURE 0F oLEFINs Filed oct. 12, 1936 3 'sheets-sheep;

Sept.5, 1939. A. 'JQ VAN PEsKl 2,172,228

PRocEss Foa THE MANUFACTURE oF oLEFINs Filed oct. 12, 193e s sheets-V-sheet 2V SePt- 5, 1939. A. J. VAN PEsKl 2,172,228

PRocEss Foa THE MANUFACTURE oF oLEFIns Filed oct. 12, 193s s sheets-sheet 3 Zia Patented Sept; 1939 UNITED STATES PATENT oEFlcE' amazes PnocEss Fon 'mE MANUFACTUBE oLEFINs Adrianus Johannes van Peski, msterdam, Netherlands, assigner to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application october 12, 1936, serial No. 105,269 In the Netherlands November 1,1935

7 claims. (o1. 26o-css) 'I'his invention is a continuatlon-in-part of my application, Serial No. 724,883, led May 10, 193,4, and deals with a 'method for cracking paraiiinic hydrocarbons under conditions to produce cracked oil which contains a high percentage -of long chain oleins of the type which are suitable i. e. for the manufacture of high viscosityindex lubricating oils by polymerization for the manufacture of high molecularalkali salts of monoalkyl sulfuric acid esters and for the manufacture of higher alcohols, ethers and the like.-

In the parent application I have disclosed a method whereby substantially pure normal olens of and more carbon atoms can be obtained. Briey, the methodconsists of cracking hydrocarbons such as normally solid parailin wax, in the vapor phase, and then subjecting cracked distillates comprising 5 carbon and higher hydrocarbons, produced in this operation, to a very eicient fractional distillatio-n. I have shown that the distillation curves of these dis` tillations, obtained by plotting boiling points' versus percent distilled, exhibit plateaus, each plateau indicating a fraction consisting essentially of a single olen, Depending upon the concentration of the parain wax in the cracking stock, the plateaus are more or less pronounced, the sharpness in general increasing with increasing wax content. The influence of the Wax content on the sharpness of the plateaus is demonstrated in the attached Fig. 1 in which 1 four distillation curves I, II, III, IV, are shown of distillates obtained by vapor phase cracking hydrocarbon oils containing 1%, 13.5%, 24% and 100% parain Wax, respectively. To enable the other purpose to provide a cracking process whereby a paraflnic distillate which contains no extraneously added wax, can be cracked to obtain optimum yields of highmolecular oleiins which, upon polymerization, produce lubricating oils of high viscosity index and areY very valuable for the manufacture of alkali salts -of monoallgvl sulfuric acid esters.

Straight chain olens boiling between about 16o-300 C, produce upon polymerization the best lubricating oils, quality being judged chiey by the viscosity index. Cyclic hydrocarbons capable of participating in the polymerization, especially aromatlcs and in particular polycyclic aromatics, if present even in small quantities, tend to lower the viscosity index of the resulting lubricating oil. Therefore, it is the aim topro-f duce a maximumyield of `a fraction boiling between about 160-300 C. which contains a maximum proportion of straight chain olens and which is substantially free from, i. e. contains' about or less cyclic hydrocarbons. I have found that good yields of the desired long chain olens can be obtained not only-froml paran Wax or oils rich in wax, i. e. vcontaining 20% or more wax, but also from vaporizable parafnic oils of thertype of kerosene, gas, oil, wax distillate, lubricating distillate, having characterization factors asdened by Watson, et al. in Ind. & Eng. Chem. vol. 27 (1935) pages 1460-1464, of at least 12.0. Such oils consist predominantly of parainic and monocyclic'hydrocarbons with long aliphatic side chains of 5' andmore carbon.

atoms, and have a relatively low content of polycyclic hydrocarbons. The content of componentscapable of sulfonation with concentrated sulfuric acid should be preferably below about 20%. As a general rule the higher the characterization factor is, the better is the yield of the desirable olefins. Parafn waxes have vthe highest characterization factors of any known hydrocarbons and consequently give best results as hereinbefore pointed out.

By solvent extracting parailinic oils their characterization factors can usually be raised materially, and their contents of polycyclic components can be decreased. Still greater improvements can be obtained by selectively dehydrogenating the oils under conditions to convert naphthenes to aromatics and then solvent-ex-v tractingthe dehydrogenated product to separate polycyclic aromatic hydrocarbons of low characterization factors from the more parainic hydrocarbons of higher characterization factors.

Cracking must be carried out in the vapor phase. Since liquid phase cracking results in a smaller yield of olefins less suitable for lubricating oil synthesis the vapors should be free from liquid entrainment to insure optimum yield and quality of the desired oleflns. Absence of en- *vtrainme'nt is alsoimportan't to 'avoid coke deposition in the cracking zone.

All conditions tending to cause substantial precracking must be avoided or at least minimized.

Such conditions include sudden pre-heating of the cracking stock, for instance, by directly mixing it with the cracked vapors for the purpose of 'quenching ,the latter, or vaporizing it at temperatures a't which substantial cracking may occur, or heating the vapors from the incipient cracking Itemperature to the optimum cracking temperature at a relatively slow rate. Thus the evaporation temperature should not exceed about 480 C., which usually necessitates the use of a distillation aid such as steam. The time required to heat the vapors from incipient cracking temperature to the maximum cracking temperature, should preferably not be longer than about 1/3 yof the total cracking time or about 11/2 seconds when cracking Within the preferred temperature range of S50-560 C. Pre-cracking appears to cause formation of branched chain olens and cyclic compounds, both of which are undesirable in the manufacture of synthetic lubricating oils.

Ana average cracking temperature of between 500 and 600 C. and preferably between 550 and 560 C. must be maintained. The vapors Ashould be held at a uniform cracking temperature for as long a. portion of the total cracking time as possible. Deviations from the optimum temperature range cause a reduction in the yield of the desired i60-300 C. fraction, or a reduction of percent olens contained therein, or both. Thus, when in a series of cracking tests, the temperatures were changed from 560 to 540 and 570 C. respectively, under otherwise optimum conditions, the yields of olens on the basis of converted cracked stock were as follows:

Average cracking temperature, "C 560 540 5 Reaction time in seconds 3. 4 6. 8 3 2 Yield of olens, volum e percent of the corresponding fraction, boiling- Up t0 300 C 39. 7 37. 1 35. 3 Up to 160 C 17. 4 15. 3 15. 9 Between i60-220 C.- 12. 0 11. l 11. 7 Between 220-300 0...-- l0. 7 7. 7

Within a temperature range of 550-560" C. the cracking time should not exceed 6 seconds and is preferably limited to between 2.5 and 5 seconds as may be seen from the following typical data:

Reaction time in seconds 8.0 3. 4 2. 2

Average cracking temperature, C 560 560 560 Yield of olefins, -volum e peroent of the corresponding fraction, borhn U 300 35. 3 39. 7 38.6 U 160 C 17. 4 14. 7 Between i60-220 C-- 12. 0 10. 5 Between 220-400 C 10. 3 13. 4

Cracking time as herein defined is computed by the approximate formula:

Tirne= Mol. wt. of cracking-rural. wt. of Y stock diluent gas in which V=vo1ume of cracking space in liters,

A=throughput of cracking stock in grams per second,

B=throughput of diluent gas in grams per second,

T==average cracking temperature in C.

the mixture 'is not more than about 60% and preferably between 30 and 50% of the total pressure in the cracking zone.

Since normally a distillation aid is required in the vaporization of the hydrocarbon oil to avoid pre-cracking, as hereinbefore explained, there will usually be enough of inert diluent present, and in general, one must guard against an excess rather than a lack of diluent. While an excess of diluent gas, if very great, may adversely affect the olefin yields, its main disadvantage lies in that it seriously reduces the charging capacity of the cracking unit.

The total pressure in the cracking zone may be varied between about l and 5 atmospheres, higher pressures tending to increase the yield of the 160-300" C. fraction, but also tending to reduce the amount of olefins contained therein.

At the end of the cracking period the cracked vapors must be abruptly cooled, preferably by quenching with water, although other quenching 'media, such as normally gaseous liquefied hydrocarbons, may also be used. The use of cracked distillates or fresh feed oil for quenching should be avoided for reasons already mentioned. In the quenching operation, the temperature of the cracked vapors should be lowered to a temperature of about 480 C. or lower, at which temperature olens are sufficiently stable to resist material isomerization or cyclization over short periods of time.

An uncracked portion of hydrocarbons contained in the quenching mixture may be recirculated through the cracking zone without danger of imparing the quality of the olefins, provided the tarry material formed during cracking is carefully separated therefrom by fractional distillation.

The means by which to accomplish the aforementioned conditions may vary. In Fig. 2, an illustrative ow diagram of a cracking process is shown, which meets the various requirements. Referring to Fig. 2, paraffin hydrocarbons from a source not shown are forced by pump I in line 2 through heating coil 3 in furnace 4, in which they are heated to a vaporizing temperature below about 480 C. Heating should be relatively gentle to avoid local overheating, a high velocity through coil 3 therefore being desirable. The heated oil is then transferred through transfer line 5 into an evaporator 6, where at least a portion of the oil is vaporized. Live steam, which is preferably superheated, or any other heated inert distillation aid such as carbon dioxide, nitrogen, hydrogen, etc. is introduced through line 'i into the evaporator 6 to aid in the vaporization of the oil. The resulting vapors, which normally contain entrainment, are now treated to eliminate such entrainment. For instance, the vapors may pass through line 8 into an apparatus 9 known as a centrix, which consists of a Vertical cylindrical vessel containing stationary blades 9' which impart to the passing vapors a whirling motion, in consequence of which the entrained liquid is thrown against the wall of the Vessel and returns to the evaporator 6; or the vapors may pass through an expansion valve I0 in line I I to effect vaporization of entrainment. and steam may be injected into line II on the low pressure side of valve I0, if desired; or the wet vapors may pass through drying coil I2 located in furnace l, where they may be heated to approximately incipient cracking temperature. if desired.

The thoroughly dried vapors proceed through line Il to cracking coil Il in furnace IB. The

first portion of the coil is located in the hottest part of the furnace in the vicinity of the bridge wall I9.. A' high vapor velocity is maintained through that portion of the coil to obtain an optimum heatv transfer. and the vapors are spontaneously heated to the required cracking temperature of about 560 C. Vapors and flue gases may flow concurrently to achieve greatest rate of heat transfer. In thelast portion of the coil. the vapors are'held at this temperature for the necessary time to eifect cracking.

The cracking vapors enter transfer line l1 in which they are quenched to below about 480 C. A suitable quenching medium, such as water, normally gaseous liquefied hydrocarbons, etc. is introduced into line I1 through line Il. The quenched mixture containing cracked distillate, gas, unconverted parafilnic hydrocarbons, tar, distillation aid and quenching medium, enters fractionator I9 in which tar and unconverted parafiinic hydrocarbons are separatedasliquids. These liquids are conveyed by pump in line 2| to evaporator 6, where paraiiinic hydrocarbons are re-evaporated and tar is allowed -to escape through bottom drain 22. 'I'he -vaporlzed portion of the charge is transferred from fractionator I9 through transfer line 23 to fractionator 24, where it is further fractionated into a heavier distillate fraction which may berun through cooler 25 in line 26 to rundown tank 21, while a light fraction passes through vapor line 28, condenser 29 into receiving tank`30, where liquid hydrocarbons are separated from gas. Gas goes through line 3| to a gas plant-not shown.

The bottom stream of fractionator 2l instead of going to storage in tank 21 may be further fractionated in a'precision column 92, provided with sidestrippers, not shown, in accordance with the invention described in the aforementioned parent application Serial No. 724,883. Several fractions, having substantially constant boiling points,i. e. at least 80% of such fractions boiling` over a temperature range of less than about 3 C., may be taken from column 32 and be passed through condensers 33-38 in lines 39-44 into tanks -50, respectively. This bottom streamv may consist entirely of such substantially boiling fractions, or may contain small intermediate fractions boiling between the larger constant boiling fractions. 'I'hese intermediate fractions may be withdrawn if desired through manifold 5I and be discarded through line 52.

In a specic example, parailin wax having a melting point of 54 C. and an average molecular weight of 390, was heated in coil 3 to 470 C. and evaporated in evaporator 6 at a pressure of 4.8 atmospheres. 10.1% by weight of steam was introduced into the evaporator through line 'l at a temperature Vof 445C. 'I'he vapors in which the partial pressure of the hydrocarbon was about lf3 of the total pressure, were passed at a pressure of 2.9 atmospheres through separator 9 lto remove entrained liquids. l

The dry vapors then were conducted through cracking coil Il in which they were rapidly heated and cracked at an average temperature of 545 C. for 2.9 seconds at an average pressure of 2.7 atmospheres. 'I'he time required to heat the dry vapors to the desired cracking temperature was about V4 ofthe total cracking time. The cracked f 3 vapors leaving the cracking furnace were quenched with water to a temperature of about 400 C. The

quenched product was fractionated in column I9 into a light fraction boiling up to 300 C. and a heavier fraction, the heavier fraction returning to evaporator 9. From the light'fraction a distiilate boiling up to 300 C. was prepared. which constituted by weight of the converted charge. This distillate had a specific gravity at 15 C. of .771 (52 A. P. I. gravity), a Mclihin'ey bromine number of 93.5 and the following A. S. T. M. distillation:

Initial boiling point or c.

165 191 221 243 2G) 275. @l 3l) from 200-300 C. from the above distillate ,wasv

subjected to an analytical distillation in a precision column, and the distillation curve shown as Fig. 3 exhibiting the typical plateaus, was thereby obtained.

According to this analysis in which 176 milliliters out of the 200 were actually distilled,- Vthe fraction was composed as follows:

on the basis or the actually distiued traction, the above total percentages are:

. Percent Normal olei'ins 87 Other hydrocarbons 13` In another cracking test, a Borneo parain distillate having a characterization factor of 12.1 was cracked under the optimum conditions hereinbefore described. A cracked fraction boiling up to 200 C. contained about 10% aromatics was rened and polymerized and yielded a lubricating oil having a viscosity index of 104. Variations from the optimum conditions, such as cracking at higher temperatures or `for longer periods of time, were immediately reected in a loss of yield of the desired olens or increase in the aromatic content of the cracked distillate or both. Thus, for instance, when cracking the same stock at 600 C. instead of 560 C. the content of aromatics in the distillate rose to above 16%, and the viscosity index of the lubricating oil produced by polymerization of the refined distillate dropped to 88.

On the other hand, when a mixture of 60% parafn wax and 40% of a highly aromatic gas oil was cracked under optimum conditions and a gasoline so obtained was polymerized, the resulting lubricating oil had a viscosity index of only 20.

The long chain oleiins which are produced when subjecting a paraiiin` oil of a low content of cyclic hydrocarbons, or mixtures of such paraftin oil with parafiin wax, to my cracking process, are useful not only for the manufacture of high viscosity index lubricating oils, but also for the production of Washing, wetting and emulsifying agents. These agents may be prepared by treating selected olens, for instance those of 13-18 carbon atoms, with sulfuric acid under conditions to produce mono-alkyl sulfuric acid esters, the alkali salts of which are known to be excellent hard Water detergents. The long chain olens may also be used for the preparation of other high molecular compounds, such as higher alcohols, ethers and the like.

I claim as my invention;

1. A process for producing olefinsl from solid paraiiins and highly paraiiinic distillates predominating in crystallizable paraiiins, which comprises vaporizing the parafnic material without substantial cracking thereof, subjecting the vapors, by indirect applicationv of heat thereto and in the presence of steam, to a temperature within the approximate range of 540 C. to 570 C. for a time period of from three to six seconds and under a pressure below 75 pounds per square inch, then promptly quenching the heated vapors to prevent continued conversion thereof, and fracticnating and condensing the vapors.

` 2. A process for producing olefins from a parafflnic hydrocarbon mixture having a boiling range not below that of kerosene and a characterization factor of at least 12.0, which comprises vaporizing the paranic mixture without substantial cracking thereof, subjecting the vapors by indirect application of heat thereto and in the presence of steam, to a temperature Within the approximate range of 540 C. to 570 C. for a time period of from 2.5 to 6 seconds and under a pressure not above 5 atmospheres, then promptly quenching the heated vapors to prevent continuedV conversion thereof, and 4fractionating and condensing the vapors.

.3. A process for-producing oleins from a paraiiinic hydrocarbon mixture having a boiling range not below that of kerosene and a characf terization factor of at least 12.0, which comprises vaporizing the paraiiinic mixture Without substantial cracking thereof, removing entrained liquid from the resulting vapors, rapidly heating by indirect application of heat the dry vapors in the presence of steam to a temperature within the approximate range of 540 C. to 570 C. for a time period of 2.5 to 6 seconds and under a pressure not above 5 atmospheres, then promptly quenching the heated vapors to prevent continued conversion thereof, and fractionating and condensing the vapors.

4. The process of claim 3 in which the partial pressure of the hydrocarbons in the vapor mixture is between 30% and 60% of the total pressure.

5. A process for producing olefins from a paraflinic hydrocarbon mixture having a boiling range not below that of kerosene and a characterization factor of at least 12.0, which comprises vaporizing the paraiiiriic mixture without substantial cracking thereof, subjecting the vapors by indirect application of heat thereto in the presence of steam and under a pressure of not above 5 atmospheres, to an effective cracking temperature within the approximate range of 540 C. to 570 C. for a time period of from 2.5 to 6 seconds, the time of heating from incipient to the effective cracking temperature being not more than one-third of the total' cracking time, then promptly quenching the heated vapors to.

prevent continued conversion thereof, and fractionating and condensing the vapors. 4

6. A process for producing olefins, suitable for the production of synthetic high viscosity index lubricating oils by polymerization, from a paraftnic hydrocarbon mixture having a boiling range not below that of kerosene and a characterization factor of at least 12.0, which comprises vaporizing the parafiinic mixture without substantial cracking thereof, subjecting the vapors by indirect application of heat thereto and in the presence of steam to av temperature within the approximate range of 540 C. to 570 C. for a time period of from 2.5 to 6 seconds and under a pressure not above 5 atmospheres, then promptly quenching the heatedA .vapors to a temperature below 480 C. to prevent continued conversion thereof, fractionating and condensing the vapors to produce a distillate comprising a fraction boiling between 160 to 300 C.

7. A process for producing olens from a parafiinic hydrocarbon mixture having a boiling range not below that of kerosene and a characterization factor of at least 12.0, which comprises heating and vaporizing the parafllnic mixture without substantial cracking thereof in a vaporization zone and with the aid of steam, removing entrained liquid from the vapor mixture, rapidly heating in a separate heating zoneby indirect application of heat the dry vapor mixture to an effective cracking temperature within the approximate range of 540 to 570 C., the total cracking time being from 2.5 to 6 seconds and the time of heating from incipient to effective cracking temperature being notmore than one-third of the total cracking time, under a pressure not more than 5 atmospheres, then promptly quenching the heated vapors to prevent continued conversion therof, and'fractonating and condensing the vapors.

ADRIANUS JOHANNES vm PESKI. 

